"The half-life of radioactive carbon (14) is 5730 years. If the amount of radioactive carbon left over after 1000 years is 5 grams, how much radioactive carbon did you start with?"

equation given to me is

Now how do I find

I've found

Mr F says: There should be no negative. Clearly a typo on your part. And you should state the accuracy that you've rounded your answer to.
Therefore I have formulated this equation

My problem is, how do I find

from the above formula or have I done something wrong. Everytime I do it, I end up with weird answer. Please help

Just out of curiosity though, my answer = 5.643124562. Is that right? or wrong?